The present invention relates to a display control/drive device for driving a display panel, and more particularly to a technique that can be effectively applied to the drive signal output system for display control/drive devices configured as semiconductor integrated circuits, for instance a technique that can be effectively applied to a liquid crystal display control/drive device for driving a low temperature poly-silicon (LTPS) liquid crystal panel and a liquid crystal display system using the device.
In recent years, a dot matrix type liquid crystal panel in which a plurality of display pixels are two-dimensionally arrayed in a matrix form has come to be used as the display device for mobile electronic apparatuses, such as mobile telephones and personal digital assistants (PDAs), and within each such apparatus, a display control/drive device (liquid crystal controller), configured as a semiconductor integrated circuit, for controlling this liquid crystal panel, a liquid crystal driver for driving the liquid crystal panel, or a display control/drive device (liquid crystal controller/driver) with a built-in driver, is mounted.
A liquid crystal driver supplies drive signals for the liquid crystal panel in synchronism with entered line output signals to provide the timings for application to source lines. In a conventional liquid crystal driver, since drive signals are supplied at the same timing from all the output terminals, currents to drive the liquid crystal panel concentrate, giving rise to a momentary flow of a large current, which invites spike-shaped noise on the power supply line and signal lines or a drop in power voltage.
Generally, an electronic device increasingly requires, as its electromagnetic environment becomes more complex, consideration of electromagnetic interference (EMI) not only in itself but also in the system in which it is a constituent part. In the aforementioned liquid crystal display device using the conventional liquid crystal driver, a large current momentarily flows because the source line of the liquid crystal panel is driven at the same time, and the resultant generation of spike-shaped noise on the power supply line and signal lines may invite EMI. In order to reduce this EMI as well, the concentration of currents to drive the liquid crystal panel should be prevented. To meet this requirement, there is proposed an invention regarding a source driver in which a plurality of source outputs are divided into two groups, such as a right half group and a left half group, and the output timings are staggered to avoid concentration of currents and thereby to restrain the occurrence of EMI (Patent Document 1).
On the other hand, liquid crystal panels available today include what is called an LTPS liquid crystal panel, which uses low temperature poly-silicon. Since a liquid crystal panel uses a glass substrate, its manufacturing process can involve no high temperature step. An LTPS liquid crystal panel uses poly-silicon into which amorphous silicon is transformed by poly-crystallization by laser annealing or otherwise, and has an advantage of permitting faster operation of transistors than amorphous silicon.
Incidentally, a color liquid crystal panel is provided with pixels of three primary colors including red (R), green (G) and blue (B), and each pixel is provided with a pixel electrode and a switching element consisting of a thin film transistor (TFT) for charging and discharging the pixel electrode. The sources of the switching elements of pixels of the same row are connected to common wiring for communicating image signals (called a source line or a data line).
In the conventional color liquid crystal panel, since each source line is provided with an external terminal, the number of external terminals increases with an increase in panel size, namely the number of display dots. As the liquid crystal panel is large relative to the display control/drive device, configured as a semiconductor integrated circuit, for driving this panel, the increase in the number of external terminals with an increase in panel size poses no serious problem. However, as the chip area and the package volume in a display control/drive device configured as a semiconductor integrated circuit increase with an increase in the number of external terminals, there is a demand for minimizing the number of external terminals.
An LTPS liquid crystal panel, since transistors can operate at high speed, can be so configured that a selector consisting of a transistor is provided on the liquid crystal panel side to have signals of pixels of three colors entered from a common external terminal on a time sharing basis. Inventions regarding a liquid crystal controller driver in which pixels of three colors are entered from a common external terminal on a time sharing basis include, for instance, what is disclosed in Patent Document 2.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-233358
[Patent Document 2] Japanese Patent Application Laid-Open No. 2004-029540